With the trend toward reduction of size and weight of electronic device, electric/electronic components are being made small and light. With such a trend toward the small and light electric/electronic components, the copper alloy materials to be used for terminals of the electric/electronic components are also made thinner and narrower in order to make the terminals small and light. For example, copper alloy sheets being used in ICs have a thickness of 0.1 to 0.15 mm.
As a result, the copper alloy material used for the electric/electronic components is required to have a higher strength. For example, copper alloy sheets to be used for connectors of vehicles are required to have such a high strength of 800 MPa or more.
Due to such a trend toward the thin and narrow electric/electronic components, the cross-sectional area of electrically conductive parts of the copper alloy material is decreased. In order to compensate for the decrease in the electrical conductivity due to the decreased cross-sectional area, the copper alloy material is required to have a satisfactory electrical conductivity of 40% IACS or more.
Additionally, the copper alloy sheets used for connectors, terminals, switches, relays, IC lead frames and the like are required to have excellent bendability (allowing 90° bending after a notching) as well as the high strength and the high electrical conductivity.
Conventionally, the 42 alloys (Fe-42 mass % Ni alloy) have been known as an example of a high-strength copper alloy material. The 42 alloys have a tensile strength of about 580 MPa, low anisotropy, and excellent bendability. However, the 42 alloys cannot satisfy high-strength requirement of 800 MPa or more. Further, the 42 alloys contain a large amount of Ni, and thus making the price expensive.
For this reason, the Corson alloys (Cu—Ni—Si-based alloy) that are excellent in the above-described properties and are also cheap are used for the electric/electronic components. The Corson alloys are alloys, in which a solid solubility limit of nickel silicide compound (Ni2Si) with respect to a copper greatly varies depending on temperature, which are precipitation hardening-type alloys that are hardened by a quenching and tempering process, and which have satisfactory heat resistance and high-temperature strength. Accordingly, the Corson alloys are used for various types of springs for electrical conduction or power lines having high-tensile.
However, the electrical conductivity and bendability of the Corson alloys may deteriorate when the strength of the copper alloy material is increased. That is, it is very difficult to make the high-strength Corson alloys have satisfactory electrical conductivity and bendability. Hence, there is a desire for a further improvement in strength, electrical conductivity, and bendability of the Corson alloys.
There have been proposed several approaches to improve the strength, electrical conductivity, and bendability of the Corson alloys. For example, according to Patent Document 1, the contents of Sn, Zn, Fe, P, Mg, Pb, as well as Ni and Si are specified so as to improve the strength and punching workability as well as the electrical conductivity, while maintaining the solder ablation resistance, heat-resistant creep property, migration resistance property, and hot workability of a bending portion.
According to Patent Document 2, the contents of Mg as well as Ni and Si and the number of precipitates and inclusions having a grain size of 10 μm or more, which are contained in the alloy, are specified so as to improve the electrical conductivity, strength, and high-temperature strength of the resulting alloy.
According to Patent Document 3, the contents of Mg and S as well as Ni and Si while controlling the content ratio of S are specified so as to suitably improve the strength, electrical conductivity, bendability, stress relaxation property, plate adhesion of the resulting alloy.
According to Patent Document 4, the content of Fe is controlled to be 0.1% or less and thus to improve the strength, electrical conductivity, and bendability of the resulting alloy.
According to Patent Document 5, the size of inclusions is controlled to be 10 μm or less and the number of inclusions having a grain size of 5 to 10 μm is controlled so as to improve the strength, electrical conductivity, bendability, etching property, and plating property of the resulting alloy.
According to Patent Document 6, the dispersion state of Ni2Si precipitates is controlled so as to improve the strength, electrical conductivity, and bendability of the resulting alloy.
According to Patent Document 7, a stretching shape of a grain of microstructures on the surface of the copper alloy sheet is specified so as to improve the abrasion-resistant property of the resulting alloy.    Patent Document 1: JP-A-9-209061    Patent Document 2: JP-A-8-225869    Patent Document 3: JP-A-2002-180161    Patent Document 4: JP-A-2001-207229    Patent Document 5: JP-A-2001-49369    Patent Document 6: JP-A-2005-89843    Patent Document 7: JP-A-5-279825